1. Field of the Invention
The present invention relates to stationery to be written upon by hand supplied in the form of a pad with many overlying sheets. The invention most particularly relates to such a pad of stationery wherein it may be desired to provide a carbon copy of what is written.
The term "carbon copy" is hereinbefore and hereinafter defined as a facsimile copy of a written message produced on a further sheet of stationery in consequence of the pressure on a first sheet of stationery during its being written.
2. The Prior Art
It is well-known in the art to provide a pad of handwriting paper in the form of a block of sheets. The sheets overlie one another and further overlie a backing card which gives stiffness to the pad. It is also well-known to provide the pad with a writing guide sheet which is detached and placed beneath a page to be written on. The guide sheet is provided with lines which are visible through the sheet to be written on and which provide guide lines for handwriting.
It is further well-known to employ a sheet of carbon paper to make a copy of a handwritten message on a subsequent sheet in such a pad of paper. Most users of such pad on some occasions wish to keep a copy of what is written in the event of its being necessary to retain a record of what is written and, on other occasions, do not require to keep a copy. As an example, if such a pad is used for personal correspondence, then letters of business may be such that it is desired to keep a record of what is written, whereas personal letters require no such record. Such pads are also preprinted and used for the writing of computer software, purchase orders, interoffice memos and the like. Depending upon the nature of the matter written on the pad, and upon whether the matter written on the pad is written by way of experimentation or as a permanent result, it may or may not be desired to keep a record. It is common practice to provide such pads with a sheet of carbon paper which can be inserted when it is desired to keep a permanent record. The carbon paper is messy, wears out, and is readily lost. It is not, therefore, convenient to provide a sheet of carbon paper with such a pad.
It is further well-known in the art to provide self-copying paper. A sheet of paper can be coated with a substance or substances which cause coloration when subjected to pressure. Two-part dies and mutually-cooperating surfaces have made it possible to coat one sheet of paper with one material, and another sheet of paper with another material, the two materials cooperating when in contact and under the influence of pressure to leave a mark on one of the sheets of paper. Examples of cooperative two-part pressure-sensitive dies and methods of encapsulating them and coating paper are to be found in U.S. Pat. No. 2,711,375, U.S. Pat. No. 2,800,457, U.S. Pat. No. 2,800,458, U.S. Pat. No. 3,041,288, U.S. Pat. No. 3,208,951, U.S. Pat. No. 3,865,613, U.S. Pat. No. 4,233,060, U.S. Pat. No. 4,263,344 and United Kingdom Pat. No. 1,232,347.
A carbon front coating and a carbon back coating are hereinafter defined as a pair of coatings for application to paper, said carbon front coating and said carbon back coating being cooperative, when brought into contact with one another and pressure applied therebetween to leave a recorded mark on said carbon front coating and not to leave a mark upon said carbon back coating.
With reference to a pad of stationery, the terms "top" and "bottom" and "upper" and "lower" are hereinafter defined as being those directions appropriately so-named when said pad is lying with its sheets of stationery in a horizontal position.